A Construction Method of an Isomorphic Map between Quadratic Extension Fields Applicable for SIDH

Abstract

A quadratic extension field (QEF) defined by F₁ = F_p[α]/(α²+1) is typically used for a supersingular isogeny Diffie-Hellman (SIDH). However, there exist other attractive QEFs F_i that result in a competitive or rather efficient performing the SIDH comparing with that of F₁. To exploit these QEFs without a time-consuming computation of the initial setting, the authors propose to convert existing parameter sets defined over F₁ to F_i by using an isomorphic map F₁ → F_i.